Developmental regulation of Thy 1.2 rate of synthesis in the mouse cerebellum

Tissue-type plasminogen activator is an extracellular mediator of Purkinje cell damage and altered gait

Purkinje neurons are a sensitive and specialised cell type important for fine motor movement and coordination. Purkinje cell damage manifests as motor incoordination and ataxia - a prominent feature of many human disorders including spinocerebellar ataxia and Huntington's disease. A correlation between Purkinje degeneration and excess cerebellar levels of tissue-type plasminogen activator (tPA) has been observed in multiple genetically-distinct models of ataxia. Here we show that Purkinje loss in a mouse model of Huntington's disease also correlates with a 200% increase in cerebellar tPA activity. That elevated tPA levels arise in a variety of ataxia models suggests that tPA is a common mediator of Purkinje damage. To address the specific contribution of tPA to cerebellar dysfunction we studied the T4 mice line that overexpresses murine tPA in postnatal neurons through the Thy1.2 gene promoter, which directs preferential expression to Purkinje cells within the cerebellum. Here we show that T4 mice develop signs of cerebellar damage within 10 weeks of birth including atrophy of Purkinje cell soma and dendrites, astrogliosis, reduced molecular layer volume and altered gait. In contrast, T4 mice displayed no evidence of microgliosis, nor any changes in interneuron density, nor alteration in the cerebellar granular neuron layer. Thus, excess tPA levels may be sufficient to cause targeted Purkinje cell degeneration and ataxia. We propose that elevated cerebellar tPA levels exert a common pathway of Purkinje cell damage. Therapeutically lowering cerebellar tPA levels may represent a novel means of preserving Purkinje cell integrity and motor coordination across a wide range of neurodegenerative diseases.

Anp32e/Cpd1 regulates protein phosphatase 2A activity at synapses during synaptogenesis

Anp32e/Cpd1, a member of the acidic nuclear phosphoprotein (Anp)32 family, is characterized by the presence of an amino terminal domain containing four leucine-rich repeats and a carboxyl-terminal low-compositional complexity acidic region. In previous studies performed to understand the biological role of Anp32e/Cpd1, we showed a predominant presence of Anp32e/Cpd1 in the nucleus. However, when Anp32e/Cpd1 is in the cytoplasm, it co-localizes spatially with protein phosphatase 2A (PP2A) near cell membranes, far from the synapses. In the present work, we show that Anp32e/Cpd1 is also present as a membrane-bound 74/76-kDa protein with a widespread distribution in the brain. We reveal that the expression, synthesis and half-life of this high-molecular-weight form of Anp32e/Cpd1 are spatially and temporally correlated with the cerebellar synaptogenesis period. We demonstrate that synaptic Anp32e/Cpd1 co-localizes, interacts and inhibits PP2A activity, and that phosphorylation of Anp32/Cpd1 is required for the Anp32e-PP2A interaction. Also, subcellular localization was shown with electronic microscopy. Finally, we examine Anp32e/Cpd1 and PP2A distribution in two ataxic mutant models, weaver and staggerer, and show that their co-localization in Purkinje cell dendrites depends on parallel fibre/Purkinje cell contacts. Based on these observations, we propose that Anp32e/Cpd1 mediates synaptogenesis process by modulating PP2A activity.

Correlation between synaptogenesis and the PTEN phosphatase expression in dendrites during postnatal brain development

The PTEN (phosphatase and tensin homolog deleted on chromosome 10) tumor suppressor gene codifies a lipid inositol 3'-phosphatase that negatively regulates cell survival mediated by the phosphatidyl inositol 3' kinase (PIP3-kinase)--protein kinase B/Akt signaling pathway. Recently, PIP3-kinase was involved in axon polarization, but PTEN functions in dendrites are uncertain. Using amino-terminal antibodies against the catalytic domain, we found a 34 kDa fragment of PTEN protein detected only in mouse brain tissue, present in neuron dendrites and spines of cerebral cortex, cerebellum, hippocampus and olfactory bulb. The PTEN-fragment reaches the synaptic fraction with a positive temporal correlation with synaptic stabilization in postnatal cerebellum and brain. In the weaver mutant mice, PTEN was absent only in the Purkinje cells dendrites that cannot receive the granule cells synaptic input. Furthermore, the activated p-Akt/PKB was present in axons but not in dendrites of mature neuron cells. P-Akt was also altered by the weaver mutation maintaining the inverse correlation with the PTEN-fragment in Purkinje cell dendrites. In contrast, the expression of this fragment was not affected by the staggerer mutation. Together, these results suggest that synaptogenesis is a necessary process for polarization in PIP3 pathway mediated by the PTEN catalytic-fragment into dendrites of CNS neurons.

The rate of Tau synthesis is differentially regulated during postnatal development in mouse cerebellum

1. Tau, which is a microtubule-associated protein, with mRNA targeted to the axon and growth cone, is involved in axonal elongation. During postnatal development in mouse, Tau expression in cerebellar granule cells is reduced afte the second postnatal week. The aim of this work was to study the regulation of the rate of the synthesis of Tau protein during the period of granule cell axonal growth in mouse cerebellum. 2. We found four [35S]methionine-labeled isoforms of Tau synthesized postnataly. Their levels remain constant from postnatal day 9 to 12 (P9-P12), and decreased by P20. 3. The rate of Tau synthesis showed differences with the rate of synthesis of total proteins. They also differ from proteins phosphatases 2A and 2B, both associated with the regulation of Tau function. In addition, the turnover of newly synthesized Tau increased at P20, compared with P9 and P12. 4. These results imply a specific developmental regulation of mRNA translation of Tau, and indicate that, after the period of synapse formation is complete, and therefore axonal growth has finished (P20), only a limited number of new Tau molecules are synthesized. This might reflect that, after synapse formation is complete, newly synthesized Tau molecules are not longer needed.

Differential expression of CPD1 during postnatal development in the mouse cerebellum

Several regulated mRNAs were detected by applying differential display to the mouse cerebellum during postnatal development. One cDNA fragment, referred to as CPD1 (GenBank U89345), was characterized and cloned. Northern blots showed maximum mRNA expression at postnatal day seven (P7). The mRNA encodes a protein of 260 amino acids. In situ RT-PCR showed that CPD1 is expressed mainly in granule cells and faintly in Purkinje cells. Polyclonal rabbit antibodies and oligobodies (oligonucleotide-based synthetic antibodies) revealed a protein of 34 kDa in Western blots. Immunohistochemistry showed not only marked nuclear staining but also mild cytoplasmic localization. Granule cells undergoing active division (P4) showed very little expression of CPD1 protein, which increases from P7 to P17. CPD1, affinity-purified using a chemically synthesized oligobody inhibits the activity of protein phosphatase PP2A but not protein phosphatase PP1. Differentiated PC12 cells also showed nuclear and cytoplasmic localization. Interestingly, maximal cytoplasmic CPD1/PP2A colocalization was observed near cell membrane regions that are far from growing neurites, and on growing cones. These results suggest that CPD1 might have an important role in cerebellar development.

Definition of a novel cellular constituent of the bone marrow that regulates the response of immature B cells to B cell antigen receptor engagement

Previously we defined a Thy1(dull) bone marrow-derived cell population that regulated fate decisions by immature B cells after Ag receptor signaling. The microenvironmental signals provided by this cell population were shown to redirect the B cell Ag receptor -induced apoptotic response of immature B cells toward continued recombination-activating gene (RAG) expression and secondary light chain recombination (receptor editing). Neither the identity of the cell responsible for this activity nor its role in immature B cell development in vivo were addressed by these previous studies. Here we show that this protective microenvironmental niche is defined by the presence of a novel Thy1(dull), DX5(pos) cell that can be found in close association with immature B cells in vivo. Depletion of this cell eliminates the anti-apoptotic effect of bone marrow in vitro and leads to a significant decrease in the number and frequency of bone marrow immature B cells in vivo. We propose that, just as the bone marrow environment is essential for the survival and progression of pro-B and pre-B cells through their respective developmental checkpoints, this cellular niche regulates the progression of immature stage B cells through negative selection.

Altered protein mannosylation in developing cerebral cortex by streptomycin

Our research objective was to characterize the biochemical effect of streptomycin during postnatal rat cerebral cortex development using a sensitive method that preserves the in situ topological relationship. We found a decrease in the mannosylation of asparagine-linked oligosaccharides without affecting polypeptide synthesis, DNA synthesis or glucose and mannose disappearance from the medium in mini-tissue units derived from P5. In addition, the rate of Dolp-GlcNAc2 Man9 Glc3 synthesis and the oligosaccharide protein transferase activity did not change in the presence of the aminoglycoside. These findings strongly suggested that the alteration of protein mannosylation occurred downstream of G3 transfer to nascent polypeptides. Further, the mini-tissue units may be useful for the assessment of neurological toxicity of antibacterial agents.

Control of transcription in the RORa-staggerer mutant mouse cerebellum: glutamate receptor delta2 mRNA

The staggerer (transcription factor RORa-deleted) mutation blocks cerebellar Purkinje cell development shortly after birth. In double mutants, the homozygous staggerer mutation can 'rescue' Purkinje cells carrying a channel-opening mutation in the Glutamate receptor delta2 (Lurcher) from apoptotic death during the third and fourth postnatal weeks. Transcript levels for the glutamate receptor delta2, a channel subunit that is found at both climbing fiber and parallel fiber synapses on cerebellar Purkinje cells, are higher in the staggerer mutant cerebellum than in the wild-type cerebellum at age 14 days. By 21 days, the wild-type level is higher, having increased tremendously while the staggerer increase is modest. The results imply that the mechanism protecting Purkinje cells in staggerer-Lurcher double mutants operates by blocking mutant receptor protein localization, rather than mRNA transcription. Between the ages 10 and 14 days, the climbing fiber innervation of Purkinje cells is known to switch from multiple to single in wild-type, but not in the staggerer mutant. Therefore, the results also suggest that the multiple innervation and the level of the receptor message are coordinated, either directly or indirectly.

Fast and sensitive method for simultaneous measurement of cell proliferation rate and drug sensitivity in rat cerebral cortex

A proliferation assay based on the production of mini-units of tissue was adopted and modified for the simultaneous determination of cell proliferation rate and the effect of genistein in rat cerebral cortex. Mini-units of tissue were produced from rat cerebral cortex immediately after killing the animal and incubated with culture medium containing 3H-methyl-thymidine during 90 min. The proliferation rate was assessed by measurement of 3H-methyl-thymidine incorporation into trichloroacetic acid insoluble material/mg of protein/min. The mini-unit method preserves the neural-cell topological relation existing in vivo and, in addition, has several additional advantages: (1) the short incubation time required limits the metabolic changes, (2) the sensitivity to drugs can be assessed simultaneously with the cell proliferation rate, (3) the complete procedure can be performed within 4-6 h, and (4) many experiments can be performed with the tissue from one animal. Genistein in doses from 10 to 100 microM inhibited cell proliferation in a concentration-dependent manner. The percentage of inhibition was highest in young animals and decreased with increasing age. This method is a powerful tool for the study of drugs with short-time onset mechanisms of action and can be useful for the screening of new drugs.